This invention relates to a yoke for an E-type coupler for a railway vehicle and, more particularly, to such a yoke having a blunt nose portion by a foreshortened length of less than 3 1/2-inches to facilitate removal of the yoke together with the draft gear from a railway vehicle as well as if desired forming the nose portion of the yoke with uniformly thick walls having smooth convex outer surfaces to strengthen and improve the service life of the yoke by avoiding deformations at the keyslot areas immediately adjacent the nose portion of the yoke.
Couplers used to connect together two railway vehicles are joined to the vehicles by way of coupler yokes. A draft gear pocket is formed in a coupler yoke to receive a draft gear assembly for dampening the pull and buff forces which must be transferred between the coupler head and the railway vehicle. A standard AAR E-Type coupler yoke is a unitary casting with a symmetrical configuration about longitudinal center planes. The yoke casting includes top and bottom straps extending between a rear end portion forming a rear draft seat and a yoke head where walls form the front of the draft gear pocket facing toward the rear draft gear seat. The area surrounded by the front draft gear wall draft gear seat and the top and bottom straps form a draft gear pocket in which a draft gear can operate to cushion the buff and pull forces occurring in train service. The keyslot walls in the yoke head diverge outwardly at each of opposite sides of the yoke. Each keyslot wall is provided with key slots extending generally parallel with the straps. Semicircular ends of the keyslots avoid a localization of forces on the casting by a horizontally arranged key used to interconnect the yoke with the shank portion of a railway coupler. Forwardly of the keyslot walls there is a nose portion which projects into a central cavity of a striker casting above a striker carrier which is an integral part of the striker casting and used to engage and support the shank of the coupler. The striker casting is secured to a center sill of the railway vehicle. Front draft lugs on the rear portion of the striker casting engage a front follower, which is a rectangular block of metal, interposed between the draft gear and the front draft lugs of the striker for transferring forces from the draft gear.
The Y40 and Y41 standard yokes for type E couplers can offer significant improvements to their operation in a railway vehicle through an improved construction of the nose portion of the yokes to overcome two problems which have been found to exist. Firstly, it is frequently a difficult and tremendous task to remove a yoke with draft gear of E-Type coupler as a unit from a railway vehicle because yoke resides at a position that is too far forwardly of the vehicle whereby the nose portion and the coupler carrier of the striker interfere during the removal process even though such interference should not occur by reason of the design of the standard parts. Secondly, deformations of the yoke casting at the yoke keyslot area are caused by loading on the keyslot peripheral rib by the key. Sometimes cracks occur in the yoke casting at the forward end of the keyslot.
It is necessary from time to time to remove the draft gear from a railway vehicle for servicing and/or replacement. It is necessary to remove the yoke with the draft gear and follower block located within the draft gear pocket thereof from the vehicle after which the draft gear can be removed from the yoke at a site remote to the railway vehicle. As is well known in the art, tremendous loads are encountered by draft gear when transmitting pull and buff forces in train service. These loads are so great that dimensional clearances established by the design not withstanding manufacturing tolerances actually change because the yoke casting stretches to such an extent that intended clearances necessary to the removal of the yoke with the draft gear in tact are reduced to a point where yoke removal is impossible.
In order to remove the yoke and draft gear from the railway vehicle, it is always necessary to compress the draft gear in the draft gear pocket approximately 1/8-inch or greater in order to provide a clearance at the front and rear draft lugs so that the draft gear and yoke assembly is free to slip out of the pocket formed in the center sill. The draft gear is usually compressed by placing a compression jack in the opening between the keyslot walls such that one part of the compression jack can push against the front follower block and thereby also an extendable member of the draft gear. The compression jack is supported by the yoke through the use of a cross member that extends through the keyslot openings in the keyslot walls. The yoke must be shifted rearwardly of the railway vehicle when an interference occurs between the nose of the yoke and the coupler carrier which prevents the lowering of the draft gear and yoke assembly passed the coupler carrier. Attempts in the past to alleviate the interference problem required the placement of a shim having a suitable thickness usually 3/8-inch or greater between the rear of the draft gear and the rear draft gear seat. This gap must be created by forcing the yoke rearwardly in a manner simulating a buff condition. The precompression force of the draft gear is resisted by rear lugs on the center sill and front draft lugs on the striker that are in a forced transmitting relation with the draft gear via the draft gear follower. The purpose of the spacer between the rear of the yoke and the draft gear is to limit forward movement of the yoke when the compression jack is operated to compress the draft gear. The draft gear is then compressed through the use of the compression jack while the spacer holds the yoke at a rearward position to relieve the front and rear draft lugs of the precompression forces developed by the draft gear. However, this procedure may not be successful because there may still be insufficient clearance between the nose portion of the yoke and the striker carrier due to, for example, stretching of the yoke during use. In order to move the yoke still further rearwardly to gain adequate clearance between the nose portion of the yoke and the striker carrier, the draft gear must be first compressed to an extent sufficient to place spacers between the front stops and the front follower. The compression jack must then be released locking the draft gear between rear stops and the front spacers and thereby slide the yoke rearwardly with respect to the striker casting. A spacer must then be placed between the rear of the draft gear and yoke rear draft gear seat which has a thickness sufficiently great to provide the necessary clearance between the nose portion of the yoke and the striker carrier. Thereafter the draft gear is then compressed so that the draft gear is out of compressive engagement between the front and rear draft lugs and the shims can be removed. This procedure is costly, time consuming and must be carried out under difficult working conditions since the yoke must be retained in the downwardly facing pocket of the center sill while ensuring access to various sites for the placement and removal of spacers and shims.
The present invention provides an improved construction for the nose portion of a yoke to alleviate the problem encountered incident to the removal thereof from a railway vehicle and, at the same time, the present invention prevents deformations in the yoke keyslot area particularly at the nose portion of a yoke which distorts and even fracture sometimes after a relatively short period of time. The service life of a yoke can be very limited particularly where a yoke is provided in a unit train coal car. The deformation to the keyslot at the nose portion can be so severe that the yoke must be replaced. The type of deformation which has been found to occur is, it is believed, only caused by loading of the keyslot peripheral rib located in the keyslot walls and used to form a connection with the horizontal key with the shank portion of the coupler. As a railway car is subject to varying track conditions, factors such as rocking and super elevations cause the mating couplers to angle with respect to the car applying a torsional force to the coupler draft assembly as well as buff or draft forces. The torsional force produces a certain magnitude of a twisting angle between the interconnected components. The components will angle freely until clearances prohibit further twisting.
A coupler can imposing a turning movement on the key while restrained in the yoke keyslot. The coupler upon continued turning movement after metal to metal contact between the key and walls of the keyslot in the yoke, will turn the yoke until interference exists between the follower block and the yoke straps. With data giving steady state train action loads normally of 200,000 pounds, restraints on further yoke twisting show, with a coefficient of friction equal to 0.2, a 40,000 pound frictional force. This force is distributed over the follower-striker lug contact which prevents the follower from twisting. In an AAR E-Type coupler shank and yoke arrangement, the maximum angle which the key can attain under these conditions is about 5.25 degrees maximum, and a minimum of about 0.75 degrees. When the maximum and minimum angling of the key is compared with possible angling of the bolster and side frames on uneven or poor quality track, it is found that the maximum bolster rock relative to the track is 7.393 degrees peak-to-peak. Side frame rock relative to bearing adapters is 15 degrees peak-to-peak when two adjacent cars rock in opposite directions. This gives rise to a possible 22.39 degree angling between coupled cars. Since the torsional angling of couplers is limited relative to each other, then the remaining torsional displacement of 22.39 degrees must be absorbed by the system. When the torsional angling is compounded with the vertical angling the draft key binds on the key-slot rib creating a point load on the rib periphery.